Sash locks for casement and awning windows are well known. Casement and awning windows are typically defined as having one or more glass panels within a sash, with the sash movable within a frame. The sash is mounted in a window frame which is defined by a head jamb on the top, a sill on the bottom and two side jambs. Typically, the sash is secured to the frame via hinges and a window operator which moveably attaches the sash to the frame.
Often, for larger casement and awning windows, a single point lock is insufficient to adequately secure the entire sash to the frame. If the window is too large for a single lock, the comers of the sash may not be pulled tightly into the frame when the window is closed and locked. Consequently, a multiple lock arrangement is typically used for larger windows.
Fleming et al, U.S. Pat. No. 4,807,914, discloses a multipoint window lock for locking a pane-carrying sash in a closed position with respect to a window frame. An operator handle is pivotally movable within the handle unit housing and carries a toothed slideblock in enmeshed engagement with a rack. The pivoting motion of the operator handle within the handle unit housing displaces the rack back and forth within the channel. The rack engages from the handle unit to a remote position in enmeshed engagement with at least one lock device which is also mounted on the frame in a recessed, substantially flush-mounted manner. The rack moves linearly and engages two locks which have gears that enmesh the rack. The linear motion of the rack causes the geared camlocks (catches) to rotate. The rotation of the camlocks engages the camlocks with the keeper, drawing the keeper into a secure position within the camlock. The Fleming et al. locking cams move in unison and engage the keepers at the same time.
Tucker, U.S. Pat. No. 5,118,145 discloses a universal lock for securing any of a variety of different design window sashes closed against any of a variety of different design window frames. The lock includes a pair of spaced keepers 62 and 70 on the window sash, and a tie bar 74 mounted to the window frame and having a pair of rollers 42 and 72 thereon. The tie bar is reciprocal along its axis to selectively move the rollers into or out of engagement with the keepers of the closed window sash to selectively lock or release the sash from the frame. A base pivotally mounts a handle member to the window frame. A coupler link is pivotally secured at one end to the handle member and has a flange at the other end pivotally secured to the tie bar. Rotation of the handle causes linear motion of the tie bar. FIGS. 5 and 6 in Tucker disclose that as the tie bar is moved linearly, the lower locking mechanism contacts the lower keeper before the upper locking mechanism engages the upper keeper.
Campbell, U.S. Pat. No. 5,653,485, discloses an improved single-actuation casement on a window-securing mechanism comprising two cams and a linking arm held in tension upon closing. The cams operate in unison in a clamshell fashion.
Billingsley, U.S. Pat. No. 4,610,472, identifies the problem of the top portion of the window bowing outward as the sash is being pulled to the closed position at column 1, lines 23-29. Billingsley discloses an improved casement window securement mechanism which includes two cams, one handle, a cam linkage and a cam linkage supporting spacer. The top cam is a reaching cam, including a cam ramp with a straight drawing portion, and cam-center and over-center positions. The reaching cam draws a catch at a rate varying with the cam angle of rotation. The securement mechanism draws and positively secures a bowed or warped casement sash.
In rotational multipoint locking systems for casement or other swinging windows, the problem therefore exists that the keeper nearest the window operator nears its corresponding respective lock device on the frame before the other keeper approaches its respective lock device. The action of the lock devices grabbing the keepers at the same time is not a smooth action because the keeper farthest from the window operator is displaced from its respective lock device when such lock device makes contact with the respective keeper.